Fertilizer Selection and Application

In this article:

• What do I need to consider when selecting a fertilizer?
• How to calculate the application rate of a fertilizer?
• Top tips for applying fertilizers.

It is also important to ensure that the environment is protected by controlling unnecessary leaching, and the potential contamination of groundwater and water sources.

What do I need to consider when selecting a fertilizer?

Grass species

Each grass species has a different tolerance to acidity or alkalinity and as such it is important that the effect of a fertilizer source on soil pH is considered. Fertilizers containing ammonium sulfate will have the most acidifying effect. Those made up of predominantly urea or ammonium nitrate will also acidify but to a much smaller degree. Potassium nitrate-based fertilizers will raise pH which can lead to a disease and weed-prone turf over time.

Soil acidification is most important in high-quality ornamental lawns dominated by fine bent and fescue species to reduce weed growth and worm casting. Lawns containing high proportions of perennial ryegrass and smooth-stalked meadow grass do not require soil acidification but if it does take place lime can be applied to counteract the effect. Perennial ryegrass dominant swards also require higher levels of nitrogen to sustain healthy growth compared with a bent fescue sward, especially where the surface is subject to any significant wear.

Soil type

Soils with a high proportion of sand will be prone to leaching and will therefore require a higher input of nutrients compared with a clay-dominant material. Controlled-release fertilizers like Landscaper Pro Full Season perform well and would be recommended in such a situation.

Maintenance

For general amenity type turf where the height of cut is above 25 mm and maintenance is less intensive, controlled-release fertilizers are very useful requiring only one or two applications over the course of the year. For high-quality ornamental lawns with a low height of cut maintenance will be intensive and as such a more sophisticated fertilizer program will be required although nitrogen inputs may well be lower.

Turf establishment

Phosphate is vital for root development and grass establishment, whether it be from seed or turf. A slow-release fertilizer with a high phosphate content (e.g., Landscaper Pro New Grass 20-20-8) and cultivated to depth is the best choice in such a situation and will encourage roots to grow deeper.

Return of clippings

For general amenity turf situations where areas are large and clippings are allowed to fly, there should be adequate quantities of nutrient being returned to the soil to support healthy grass growth.

Type of fertilizer: liquid

Liquid fertilizer formulations are very good at providing small quantities of nutrient to give more control over growth and are well suited as part of an overall fertilizer program for manipulating the appearance of high-quality ornamental lawns.

Type of fertilizer: granular

Solid fertilizer formulations in granular form are very common, and come in a huge range of analyses and different technologies. They need to be applied over the turf very evenly, usually with a pedestrian spreader. Following irrigation or rainfall the granules move to the base of the grass plant where they release their nutrients into the soil to be taken up by the plant roots.

Granular – conventional fertilizer

Conventional granular fertilizers are often simple forms of nutrients. The granules dissolve in water (rainfall or irrigation) and the nutrients are immediately available for plant uptake. They allow a fast plant response, but can be used up quickly, or washed below the root level, or lost from the soil after heavy rainfall.

Granular – controlled-release fertilizer

These are designed to release nutrients in line with growth and conditions (particularly soil temperature). They can be applied in spring when soil temperatures are low allowing the subsequent passage of machinery to push the granules into the soil where the nutrients can be released as required.

Granular – organic fertilizer

These need an “active” soil to break down and release nutrients. If an immediate improvement in growth is required at a time when soil temperatures remain low (< 10⁰C) a more soluble material should be used.

How to calculate the application rate of a fertilizer?

Solid fertilizers vs. liquid fertilizers

Information concerning the appropriate application rate of a fertilizer are contained on the product packaging. There may be circumstances, especially when trying to compare the relative cost/benefit of different fertilizer products, that require you to work out the level of nutrient being applied. The calculations for this are relatively straightforward:

The nutrient ratio of a solid fertilizer is displayed on the product label e.g., Landscaper Pro All Round 24−5−8+2% MgO. The rate of the application of each nutrient is therefore calculated as a percentage of the overall application rate. For example:

Recommended application rate = 250 kg/ha

Therefore           24/100  (nitrogen) ´ 250 = 60 kg nitrogen per application

5/100   (phosphate) ´ 250 = 12.5 kg phosphate per application

8/100   (potassium) ´ 250 = 20 kg potassium per application

Calculating the quantity of nutrient applied within a liquid fertilizer formulated on a weight-to-weight (w/w) basis is completed in the same way as demonstrated for solid fertilizers above. Where liquids have a weight-to-volume (w/v) formulation the specific gravity of the product is required to allow an accurate calculation of nutrients to be calculated.

Top tips for applying fertilizers

1. Always ensure that a fertilizer is applied evenly to ensure that the treated turf does not subsequently develop uneven growth, and in some cases, turf scorch.
2. Apply during a dry interlude in showery weather. This will help ensure that the applied material is well washed into the upper soil. If no rain falls the material should be watered in, especially on fine turf which is more susceptible to turf scorch.
3. Granular fertilizers can be spread by hand to small areas but for larger turf areas there are a range of distributors available. Although such distributors come with calibration marks and guidance it is best practice to calibrate all machines on-site prior to use.
4. When applying fertilizer using a drop spreader the quantity should be divided in two and two runs made across the area—the second run being at 90 degrees to the first.
5. Rotary spreaders tend to apply more material to the middle of the spread. To avoid uneven application, the width of coverage achieved by the unit should be measured when set to apply at half the required rate. Marker posts can then be used to ensure that each successive pass is set at half the width covered by the spinner.
6. Liquid fertilizers should be applied using a walk-over or vehicle-mounted spraying unit; these have the advantage of applying fertilizer without any granules being left on the turf surface. In general, however, the amount of nutrient applied in a single operation is significantly lower compared with an application of granular material and therefore a greater number of applications is required to achieve the same level of nutrient input.
7. A liquid should be applied as a single run using marker posts to ensure there are no overlaps.